Engine/Transmission (1998.5 - 2002) Very slight rpm fluctuation, is this normal?

[CEdwards]

I just recently became a 24 valve owner after owning two 12 valve trucks. The first thing I did was add a fuel pressure gauge. Show 17 at idle 12 at 70mph. I noticed a very slight rpm fluctuation when cruising the highway. It probably wouldn't be noticeable to most people, but I noticed right away. I have been studying the threads for about a month now and I ran across an old thread where about vp44 failures and someone mentioned that after replacing IP their fluctuation went away. Is this just the nature of the electronic setup or is this an indication of a problem? Truck is a 2001 HO 6speed.

 

[blacksheepdiesel]

I have been watching mine fluctuate for 550,000+ miles. Numerous APPS, 3 VP44's, 2 ecm's, etc. , still doing it...

It could drive an extremely anal person over the edge. Glad I ain't one!

Godspeed,
Trent

 

[PC12Driver]

For mine, the rpm flutter @ cruise was due to a noisy spot on the APPS. It would sort of go away after cycling the throttle pedal a bunch of times (like twisting a volume knob on a radio back and forth to "clean" the pot), but would come back after a few trips. I could also see it in the tach if I slowly added throttle in neutral. I'd get a flutter or the rpms would hang between 1700-1900 rpm (where the APPS spends the most time and gets the most wear). Finally, sometime in the early 2001 model year the manual trucks stopped using a vacuum motor to drive the cruise control. The ECM handled the cruise internally, thus bypassing the APPS. If you have a truck with electronic cruise (probably do), the surging should go away with the cruise engaged if the APPS is at fault.



No, it's not the nature of the electronic setup.

 

[BarryG]

ditto above except mine doesnt do it all the time just some of the time. While I am anal just not extremely, this is one I have put the blinders on otherwise I would be in a room with rubber wallpaper.



Assuming there are no codes that might lend themselves to this type of issue such as cam sensor or pump code I wouldnt worry about it. By the way I have mechanical fuel supply pump and it didnt make it go away.

 

[CEdwards]

I appreciate the response and will just consider this "normal" and forget about it. Thanks guys.

 

[Moose Truck]

I appreciate the response and will just consider this "normal" and forget about it. Thanks guys.

Good to see that I am not about to have a problem with my truck, It has a slight tach flutter @ 1900 RPM. Bad to see that I am anal, good to see that I'm not that anal, I still need to wax the truck. Moose

 

[CEdwards]

It has been cooler this week and my surging seems to be getting worse. It doesn't matter if the engine is cold or operating temperature. I can really feel it defueling now. When I accelerate it will go away for a minute. Tried driving all different speeds and it still does it. After a little search on here I'm guessing it could be apps, speed sensor, bad ground or something. Can anyone point me in the right direction.

 

[CEdwards]

Forgot to mention it doesn't do it with the cruise on and this problem has been happening since the abs light started staying on. What does this point to?

 

[BarryG]

Ok now this is different from what I interpreted from your original post.



I as well have run across this on my 01. When it was doing this the most noticeable for me my vp44 went out not too long after (within 6 months). However it would do it cruise on or off and generally only seem to do it when cruising in cold temps. Kinda of like the timing was changing, it was a consistent 1 or 2 second cycle, you couldnt really see the rpms change but you could definitely hear the change. Seemed the colder it was the more pronounced it was. Vp went out that summer and the next winter it wasnt doing it.



Next time it did it it was more random not the same pattern as the first time. Vp went out again replaced it and it still did it but did end up going away on it s own.



Then I started having a miss occassionally and it would set a cam sensor code. RPMs would fluctuate and sometimes would just drop to zero momentarily. Generally it would just miss, but sometimes it would do it really bad. Only seemed to do it at idle or low rpm. I checked and cleaned all the grounds, replaced the cam sensor and no joy, swapped in an ecm again no joy, tested the wires between the cam sensor and the ecm, the ecm and the vp44 for continuity and resistance did dodges super technical wire wiggle test while doing that as well still no joy. Checked the pins on the ends of the harness in the plugs and the ecm plug still nothing. Was finally going to take it to the dealer but was waiting for it get bad enough that it was consistent. Didnt want to pay to hear them say could not duplicate. In any case I was under the hood one day doing oil change etc and remembered reading about the alternator wires causing some people some problems of various sorts. I took a look at them they looked fine but I played with them a bit seperated them apart thinking that was waste of effort. However since that day it has not acted up again. Now my problem was different than yours is now but you might give it a shot seems the alternator wires can give some wierd symptoms.

 

[blacksheepdiesel]

CEdwards,

The only part eliminated from the equation when the cruise is on is the APPS. Replace it.

Godspeed,
Trent